It varied from country to country and from period to period. But generally the average European newspaper would have been a quarto format. Some English newspapers pioneered the usage of the folio format following the Stamp Act of 1712, but this format didn't catch on in general outside the UK until the 19th century.

For most of the century the main content of European newspapers would have been foreign news. Especially in absolute monarchies there was usually restrictions on domestic news, mainly official announcements or royal festivities would be allowed to be reported, an absolutely no commentaries on news either, so they would be reported in a very neutral style.

Again there were exceptions, not least in the UK where their particular historical development saw the advent of party political press, which often contained a lot of commentary and infights regarding hot contemporary topics. But usually political commentary was presented in pamphlet form and later in the century in journals and periodicals, both in the UK and on the Continent.

In France the political press virtually exploded during the Revolution and among other things saw the advent of the first usage of shorthand by reporters present at the discussions in the National Assembly.

I can recommend the relatively new book by Andrew Pettegree, The Invention of News - How the World Came to Know About Itself, Yale University Press, 2015, which covers European news reporting from before the invention of the printing press to the end of the 18th century. Pettegree connects the importance of the invention of the postal systems with the growth of the press, and also focuses on the lesser known, but still very important early forerunners of news reporting, the news sheets, the manuscript news letters and the news serials, as well as the newspaper itself and its development in the various countries of Europe.